As is known in the art of semiconductor processing, semiconductor substrates are susceptible to contamination that may degrade their electrical properties. In particular, although a semiconductor substrate initially may a relatively high purity when it is formed, subsequent processing of that substrate may introduce contamination. For example, silicon substrates of about 99.9999999% purity may be formed using known techniques, such as the Czochralski process. However, exposing that substrate to multiple materials processing steps, such as may be performed when fabricating electronic circuitry on the substrate, may contaminate the substrate with one or more elements, such as calcium, iron, or sodium. Additionally, the electronic circuitry itself may contaminate the semiconductor substrate over time. For example, FIG. 1A illustrates semiconductor substrate 110, upon which exemplary electronic circuitry 120 is disposed, and in which one or more active (doped) regions 111 may be defined. Electronic circuitry 120 may include conductive electrodes or interconnects, generally designated 121, which may be formed of a metal such as aluminum or copper. As illustrated in FIG. 1B, materials within electronic circuitry 120, and in particular conductive electrodes or interconnects 121, may diffuse into substrate 110 as contamination 130. In some circumstances, hydrogen also may be a contaminant. Among other things, such contamination may alter the semiconductive properties of active regions 111 and potentially may interfere with those regions' functionality.
Several methods, which may be referred to as “gettering,” have been developed for reducing contamination within regions of semiconductor substrates. For example, the backside of a semiconductor substrate (the major surface opposite that upon which electronic circuitry 120 may be disposed) may be treated in a variety of ways intended to attract, or “getter,” contamination. Such treatment may include damaging the backside of the substrate, such as with a laser beam or mechanical abrasion, so as to induce stress at that surface. Subsequently annealing the substrate may create dislocations within the crystal structure of the substrate that may attract and bind, or “getter,” contaminants away from the circuitry-side of the substrate. Or, for example, the backside of the substrate may be exposed to a source of phosphorous so as to generate dislocations within the crystal structure of the substrate that may getter contaminants away from the circuitry-side of the substrate. Or, for example, the substrate may be treated so as to have a suitable percentage of oxygen therein, and subsequently may be treated to cause that oxygen to precipitate out as clusters that generate dislocations that may getter contaminants away from electronic circuitry 120 and active regions 111. FIG. 1C illustrates substrate 110′ which has been modified to include treated region 112 on the backside of substrate 110′. Treated region 112 has been damaged, exposed to phosphorous, or otherwise treated so as to getter contamination 130 out of circuitry-side region 113, which may be referred to as a “denuded zone,” and into contaminated region 114, which is disposed beneath circuitry-side region 113. Region 112 of substrate 110′ may be treated before electronic circuitry 120 is disposed on the substrate.
Gettering methods such as described above may require relatively harsh treatments to the entire semiconductor substrate, and may reduce the mechanical stability of the semiconductor substrate. Thus, what is needed is an improved method for gettering materials disposed within a semiconductor substrate, and more generally for transporting materials disposed on or within a semiconductor substrate.